<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>表格边框重叠处理</title>
  <style>
    ul {
      width: 700px;
      /* margin: auto; */
      list-style: none;
      padding: 0;
      border: 2px solid black;
      text-align: center;

    }
    li+li {
      border-top: 2px solid black;
    }
  </style>
</head>
<body>
  <ul>
    <li>1</li>
    <li>2</li>
    <li>3</li>
    <li>4</li>
    <li>5</li>
    <li>6</li>
    <li>7</li>
  </ul>
</body>
</html>